Fuel cells electrochemically convert fuels and oxidants to electricity, and fuel cells can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid, or solid polymer) used to accommodate ion transfer during operation. Moreover, fuel cell assemblies can be employed in many environments, for multiple applications.
A Proton Exchange Membrane (hereinafter "PEM") fuel cell converts the chemical energy of fuels such as hydrogen and oxidants such as air/oxygen directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (i.e., H.sup.+ ions) from the "anode" side of a fuel cell to the "cathode" side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air/oxygen gases). Some artisans consider the acronym "PEM" to represent "Polymer Electrolyte Membrane." The direction, from anode to cathode, of flow of protons serves as a basis for labeling an "anode" side and a "cathode" side of every layer in the fuel cell, and in the fuel cell assembly or stack.
Usually, an individual PEM-type fuel cell has multiple, generally transversely extending layers assembled in a longitudinal direction. In the typical fuel cell assembly or stack, all layers which extend to the periphery of the fuel cells have holes therethrough for alignment and formation of fluid manifolds that generally service fluids for the stack. As is known in the art, some of the fluid manifolds distribute fuel (e.g., hydrogen) and oxidant (e.g., air/oxygen) to, and remove unused fuel and oxidant as well as product water from, fluid flow plates which serve as flow field plates for each fuel cell. Also, other fluid manifolds circulate coolant (e.g., water) for cooling.
As is known in the art, the PEM can work more effectively if it is wet. Conversely, once any area of the PEM dries out, the fuel cell does not generate any product water in that area because the electrochemical reaction there stops. Undesirable, this drying out can progressively march across the PEM until the fuel cell fails completely. So, the fuel and oxidant fed to each fuel cell are usually humidified.
However, an overabundance of water in the fuel cell may impede delivery and removal of gases for the PEM. It is therefore desirable that excess product water and/or excess humidification water be carried away from the PEM.
Furthermore, the fuel cell may experience reactant starvation when gases besides the reactant gases are supplied to the fuel cell. With respect to the cathode side of the fuel cell, one may choose to use air rather than pure oxygen for reasons such as increased availability and/or decreased combustibility. When air is supplied as the oxidant source, the oxygen is consumed in the electrochemical reaction. But, other components of the air, such as inert gases (e.g., nitrogen and/or carbon dioxide), may linger near the PEM. Undesirably, the inert gases may impede supply of oxygen to the PEM. Such a condition may be referred to as "nitrogen blanketing" and/or "carbon dioxide blanketing."
With respect to the anode side of the fuel cell, one may wish to use propane as an original source of fuel rather than pure hydrogen, since propane may be more readily available. The propane may be passed through a reformer, the output of which may be referred to as "reformate." The reformate includes hydrogen as well as extra, undesired gases such as nitrogen and carbon dioxide, which can adversely affect performance of the fuel cell assembly. In particular, hydrogen may be consumed in the electrochemical reaction, with undesired components (e.g., inert gases such as nitrogen and/or carbon dioxide) remaining near the PEM, and undesirably impeding delivery of additional hydrogen thereto.
Thus, a need exists for a mechanism for extinguishing undesired gas and/or liquid from a flow field (e.g., a gas diffusion layer) of a fuel cell. A further need exists for such a mechanism to perform without interfering with operation or degrading output of the fuel cell. An additional need exits for increasing power density of the fuel cell, for instance, at high current density.